Process for preparing alkoxylated fatty acid alkyl esters

ABSTRACT

PCT No. PCT/EP97/01326 Sec. 371 Date Sep. 25, 1998 Sec. 102(e) Date Sep. 25, 1998 PCT Filed Mar. 17, 1997 PCT Pub. No. WO97/35830 PCT Pub. Date Oct. 2, 1997A process for making alkoxylated fatty acid alkyl esters involving: (a) providing a fatty acid alkyl ester; (b) providing an alkylene oxide component; (c) providing a catalyst component containing a mixture of: (i) a primary catalyst; and (ii) an alkylene glycol having from 2 to 6 carbon atoms; and (d) reacting (a)-(c) to make the alkoxylated fatty acid alkyl ester.

This application is a 371 of PCT/EP92/01326 filed Mar. 17, 1997.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for the alkoxylation of fatty acidalkyl esters in the presence of a homogeneous catalyst/co-catalystsystem.

2. Discussion of Related Art

Alkoxylated alkyl esters, preferably so-called methyl ester ethoxylates,are known nonionic surfactants which have recently acquired considerableinterest by virtue of their excellent washing performance. Relevantreviews can be found, for example, in J. Am. Oil Chem. Soc. 56, 873(1979) and in J. Am. Oil Chem. Soc. 72, 781 (1995).

The addition of alkylene oxides onto compounds containing acidichydrogen atoms, preferably onto primary alcohols, can be carried out inthe presence of various, generally alkaline catalysts. Typical examplesare potassium hydroxide or sodium methylate, which are added in the formof alcoholic solutions, or heterogeneous layer compounds of thehydrotalcite type which are introduced into the reaction mixture in theform of solids. By contrast, the insertion of alkylene oxides into thecarbonyl ester bond is far more difficult and can only be achieved usingspecial catalysts.

The use of calcined or fatty-acid-modified hydrotalcites for theethoxylation of fatty acid esters is known from EP-B1 0 339 425 andEP-B1 0 523 089 (Henkel). According to DE-A1 44 46 064 (Lion), theethoxylation of methyl esters is carried out in the presence of mixedmetal oxides which have been surface-modified with metal hydroxides ormetal alkoxides. However, these processes have a number ofdisadvantages. The use of heterogeneous catalysts, i.e. catalysts whichare insoluble in the reaction mixture, is technically more complicatedbecause the solid cannot be introduced like a liquid through anautomatic metering unit, but generally has to be scooped into thereactor by hand. Removal of the catalyst is also problematical becausethe catalyst particles are generally so fine that they can only befiltered through special filter candles. However, the catalyst cannot beleft in the reaction mixture either because otherwise clouding andsedimentation can occur. From the performance point of view, the resultsobtained with heterogeneous catalysts are not always satisfactoryeither. Thus, although the reaction is generally very quick, theproducts obtained normally have hydroxyl values well below thetheoretical value. As a result, products with undesirably high cloudpoints are obtained. However, since nonionic surfactants only developoptimal washing performance above their cloud point, there is a need foralkoxylated alkyl esters with as low a cloud point as possible.

Accordingly, the problem addressed by the present invention was toprovide new catalysts for the alkoxylation of fatty acid alkyl esterswhich would be free from the disadvantages mentioned above and which, onthe one hand, would dissolve in the reaction product and, on the otherhand, would give products having improved hydroxyl values and lowercloud points.

DESCRIPTION OF THE INVENTION

The present invention relates to a process for the production ofalkoxylated fatty acid alkyl esters corresponding to formula (I):##STR1## where R¹ CO is a linear or branched acyl group containing 6 to22 carbon atoms and 0 and/or 1, 2 or 3 double bonds, R² is hydrogen or amethyl group, R³ is a linear or branched alkyl group containing 1 to 22carbon atoms and n is a number of--on average--1 to 20,

in which mixtures of

(a) alkali metal and/or alkaline earth metal hydroxides and/oralcoholates and

(b) alkylene glycols

are used as catalysts.

Whereas alkali metal hydroxides on their own do not catalyze thealkoxylation of alkyl esters and the use of alkali metal alcoholatecatalysts leads to products with a very high cloud point, it hassurprisingly been found that the addition of alkylene glycols to thesecatalysts significantly improves activity and/or selectivity. However,the use of the system according to the invention of homogeneous catalystand co-catalyst surprisingly leads to alkoxylated alkyl esters whichhave a hydroxyl value near the theoretical value and which aredistinguished by a very low cloud point.

Fatty acid alkyl esters

The fatty acid alkyl esters used as starting materials are derived fromsaturated and/or unsaturated fatty acids containing 6 to 22 andpreferably 12 to 18 carbon atoms and alcohols containing 1 to 22 andpreferably 1 to 4 carbon atoms. Typical examples are methyl, ethyl,propyl, butyl and/or stearyl esters of caproic acid, caprylic acid,2-ethylhexanoic acid, capric acid, lauric acid, isotridecanoic acid,myristic acid, palmitic acid, palmitoleic acid, stearic acid, isostearicacid, oleic acid, elaidic acid, petroselic acid, linoleic acid,linolenic acid, elaeostearic acid, arachic acid, gadoleic acid, behenicacid and erucic acid and the technical mixtures thereof obtained, forexample, in the pressure hydrolysis of natural fats and oils or in thereduction of aldehydes from Roelen's oxosynthesis. Cocofatty acid and/ortallow fatty acid methyl esters are preferably used as startingmaterials.

Catalysts

Catalyst component (a) may be selected from alkali metal hydroxides,alkaline earth metal hydroxides, alkali metal alcoholates and/oralkaline earth metal alcoholates. Typical examples are sodium hydroxide,potassium hydroxide, magnesium hydroxide, calcium hydroxide, bariumhydroxide, sodium methylate, potassium tert.butylate, calcium ethylateand/or magnesium methylate. Potassium hydroxide and/or sodium methylateis/are preferably used. The catalysts (a) are used in quantities ofnormally 0.1 to 1.5% by weight and preferably 0.4 to 1% by weight, basedon the end products.

Catalyst component (b), i.e. the co-catalyst, may be selected fromalkylene glycols containing 2 to 6 carbon atoms, for example ethyleneglycol, diethylene glycol, propylene glycol and/or dipropylene glycol.The co-catalysts are used in quantities of normally 0.5 to 5% by weightand preferably 1 to 4% by weight, based on the end products.

Alkoxylation

The alkoxylation reaction may be carried out in known manner. To thisend, the alkyl ester is normally introduced into a stirrer-equippedautoclave and the homogeneous catalyst is subsequently added, forexample in the form of a solution in water, but preferably in methanol.It has proved to be of advantage to purge the autoclave thoroughly withnitrogen before the reaction to remove all traces of atmospheric oxygenand to remove methanol used as solvent by evacuation. The autoclave isthen heated. The alkoxylation reaction is carried out at temperatures ofpreferably 140 to 180° C. and more preferably 160 to 170° C. Thealkylene oxide, which may be ethylene oxide, propylene oxide or mixturesof both, is introduced into the reactor by a siphon. The autogenouspressure can rise to about 5 bar. The alkylene oxide, preferablyethylene oxide, is preferably used in a quantity of on average 1 to 20moles and more preferably 8 to 15 moles per mole of alkyl ester. Theaddition of the alkylene oxide is statistical, i.e. the insertion is nota highly selective reaction in which 1 mole of fatty acid alkyl esterreacts with exactly n moles of alkylene oxide. Instead, a complexmixture of esters alkoxylated to different degrees is obtained. Thereaction is over when the pressure in the reactor falls to about 0.5bar. For safety reasons, it is advisable to stir the mixture for another30 minutes before the reactor is cooled and vented. If desired, thealkaline catalyst can be neutralized by the addition of acids, forexample phosphoric acid, acetic acid, lactic acid or the like.

COMMERCIAL APPLICATIONS

The alkoxylated fatty acid alkyl esters obtainable by the processaccording to the invention have hydroxyl values near the theoreticalvalue and are distinguished by comparatively low cloud points.Accordingly, in relation to known comparable products which have beenobtained using other catalysts, optimal washing performance is achievedat lower temperatures.

EXAMPLES

General procedure. 256 g (1 mole) of technical C_(12/16) cocofatty acidmethyl ester were introduced into a 1-liter stirred autoclave and theproposed quantity of catalyst in the form of a solution in methanol (ca.30% by weight) was added. The autoclave was closed and then alternatelypurged with nitrogen and evacuated three times to rule out the presenceof atmospheric oxygen and to remove the methanol solvent. The reactionmixture was then heated to 165° C. under a nitrogen blanket and 484 g(11 moles) of ethylene oxide were introduced in portions, the autogenouspressure initially rising to 3.5 bar. The reaction was continued untilthe pressure had fallen to 0.5 bar. After stirring for another 30minutes, the autoclave was cooled and vented.

The results of the tests are set out in Table 1. The quantities ofcatalysts used are based on the end product. The theoretical hydroxylvalue was 23.2.

                                      TABLE 1                                     __________________________________________________________________________    Ethoxylation of cocofatty acid methyl ester                                               [Cat.]       [Co-cat.]   Cl. P.                                     Ex. Catalyst % by wt. Co-catalyst % by wt. S.V. OH V. ° C.           __________________________________________________________________________    1 Potassium hydroxide                                                                     0.4  Ethylene glycol                                                                       3.8  77.4                                                                             29.3                                                                              53.0                                       C1 Calc. hydrotalcite 1.0 None --  79.4 6.4 64.5                              C2 Potassium hydroxide 1.0 None -- * * *                                      C3 Potassium hydroxide 1.0 Lauric acid 0.5 * * *                              C4 Sodium methylate 1.2 None --  73.1 21.2 6.0                                C5 Sodium methylate 0.8 Methoxy ethanol 0.33 75.4 14.7 70.5                 __________________________________________________________________________     Legend:                                                                       S.V. = Saponification value                                                   OH V. = OH value                                                              Cl. P = Cloud point                                                           * = No reaction                                                          

We claim:
 1. A process for making alkoxylated fatty acid alkyl esterscorresponding to formula ##STR2## wherein R¹ CO is a linear or branchedacyl group containing from 6 to 22 carbon atoms and up to 3 doublebonds, R² is hydrogen or a methyl group, R³ is a linear or branchedalkyl group containing from 1 to 22 carbon atoms and n is a number offrom 1 to 20, the process comprising:(a) providing a fatty acid alkylester; (b) providing an alkylene oxide component; (c) providing acatalyst component containing a mixture of:(i) a primary catalystselected from the group consisting of an alkali metal hydroxide, analkaline earth metal hydroxide, an alkali metal alcoholate, an alkalineearth metal alcoholate and mixtures thereof; and (ii) an alkylene glycolhaving from 2 to 6 carbon atoms; and (d) reacting (a)-(c) to make thealkoxylated fatty acid alkyl ester.
 2. The process of claim 1 whereinthe primary catalyst is employed in a quantity of from 0.1 to 1.5% byweight, based on the weight of the alkoxylated fatty acid alkyl ester.3. The process of claim 1 wherein the primary catalyst is employed in aquantity of from 0.4 to 1.0% by weight, based on the weight of thealkoxylated fatty acid alkyl ester.
 4. The process of claim 1 whereinthe alkylene glycol is employed in a quantity of from 0.5 to 5% byweight, based on the weight of the alkoxylated fatty acid alkyl ester.5. The process of claim 1 wherein the alkylene glycol is employed in aquantity of from 1 to 4% by weight, based on the weight of thealkoxylated fatty acid alkyl ester.
 6. The process of claim 1 whereinthe reaction is carried out at a temperature of from 140 to 180° C. 7.The process of claim 1 wherein the alkylene oxide component is ethyleneoxide.
 8. The process of claim 1 wherein the alkylene oxide component isemployed in a quantity of from 1-20 moles of alkylene oxide per mole ofalkyl ester.